Casing mounted sensors, actuators and generators

ABSTRACT

A casing sensor and methods for sensing using a casing sensor are disclosed. The casing sensor includes a casing shoe and a sensor coupled to the casing shoe. A casing data relay includes a downhole receiver coupled to a well casing and a transmitter coupled to the receiver. The casing sensor may be coupled to the transmitter. A drill string actuator may be controllable through the downhole receiver.

FIELD OF THE INVENTION

[0001] This invention relates generally to a method and apparatus forcollecting data regarding geological properties of underground orundersea formations in the vicinity of a well bore under construction.More particularly, this invention relates to a method and apparatus forcollecting data regarding the formations during and after drilling andconstructing the well bore. In particular, the invention relates to amethod and apparatus for collecting data regarding the formationssensors, actuators and generators coupled to a well casing inside thewell bore. This invention also relates to a method and apparatus forrelaying data collected deep in a well to the surface.

BACKGROUND OF THE INVENTION

[0002] Geologists and geophysicists collect data regarding undergroundformations in order to predict the location of hydrocarbons such as oiland gas. Traditionally, such information is gathered during anexploration phase. In recent years, however, the art has advanced toallow the collection of geophysical and geological data as a well isbeing drilled.

[0003] For example, in Vertical Seismic Profiling (“VSP”), drillingoperations are interrupted to place a series of seismic sensors atdiscrete depths in a borehole. A surface source releases energy that isreflected off underground geological formations. The seismic sensors inthe borehole sense the reflected energy and provide signals representingreflections to the surface for analysis.

[0004] In a subsequent development, known as “drill bit seismic”,seismic sensors are positioned at the surface near the borehole to senseseismic energy imparted to the earth by the drill bit during drilling.This sensed energy is used in the traditional seismic way to detectreflections from underground geological formations. Further, thistechnique is used to detect “shadows”, or reduced seismic energymagnitude, caused by underground formations, such as gas reservoirs,between the drill bit and the surface sensors.

[0005] A greatly simplified description of those steps involved indrilling an oil well follows. A portion of the oil well is drilled usinga drill string consisting of drill pipe, drill collars and drill bit.After a portion of the well has been drilled, a section of casing, orlarge bore pipe, is inserted into the well bore and cemented for, amongother things, zonal isolation. Casing performs a number of functions,including: preventing the bore hole from caving in; preventing fluids inthe bore hole from contaminating the surrounding formations; preventingthe introduction of water into the surrounding formations; containingany production from the well; facilitating pressure control; providingan environment for the installation of production equipment; andproviding zonal isolation.

[0006] When the casing is in place it is cemented to the formation wall.This is accomplished by pumping cement through the casing until it exitsat the end of the casing through a special section of casing called a“casing shoe” and flows up the annulus between the casing and the wallof the well bore. The concrete is then allowed to set.

[0007] In subsequent drilling operations, the deep end of the newlycemented casing is drilled out and another section of the well bore isdrilled. The process of drilling sections of the well bore followed byinserting and cementing well casing repeats until the desired well depthis reached.

[0008] As the well bore is being drilled, drilling fluids, known as“mud”, are pumped into the drill string. The mud travels down the drillstring until it is ejected. The mud picks up cuttings and carries themto the surface. The specific gravity of the drill mud is carefullycontrolled so that the weight of the column of mud is (1) large enoughto prevent gas or other hydrocarbons from entering the borehole from thesurrounding formations; (2) without exerting so much pressure that thesurrounding formations are damaged.

[0009] After each section of casing is laid and cemented in, thefracture pressure of the formation just below the end of the casing ismeasured. Generally, the fracture pressure of deeper formations isgreater than the fracture pressure of shallower formations. The specificgravity of the drilling mud is subsequently controlled to make sure thatthe pressure on the formation at the end of the casing does not exceedthe fracture pressure of the formation at that point. This is generallyaccomplished by calculations incorporating the measured specific gravityof the drilling mud and the depth of the column of drilling mud abovethe formation.

[0010] Downhole data are captured using “wireline” techniques in which,prior to casing being laid, a tool, such as an acoustic logging tool, islowered into the well bore and slowly retrieved, gathering data andstoring it or transmitting it to the surface as the tool is beingretrieved. Alternatively, measurement while drilling (“MWD”) or loggingwhile drilling (“LWD”) tools are attached to the drill string just abovethe drill bit and drill collars. These generally expensive tools gatherdata during the drilling process and store it or transmit it to thesurface.

SUMMARY OF THE INVENTION

[0011] In general, in one aspect, the invention features a casing sensorcomprising a casing shoe and a sensor coupled to the casing shoe.

[0012] Implementations of the invention may include one or more of thefollowing. The sensor may comprise a pressure sensor. The sensorpressure may comprise a pressure transducer and a transmitter coupled tothe pressure transducer. The casing sensor may comprise a surfacereceiver coupled to the transmitter. The casing sensor may comprise adrill string through the casing shoe.

[0013] In general, in another aspect, the invention features a casingdata relay comprising a downhole receiver coupled to a well casing and atransmitter coupled to the receiver.

[0014] Implementations of the invention may include one or more of thefollowing. The casing data relay may comprise a surface receiver coupledto the transmitter. The surface receiver may be electrically oroptically coupled to the transmitter. The surface receiver may becoupled to the transmitter by electromagnetic telemetry. The surfacereceiver may be coupled to the transmitter by a pressure transducer. Thecasing data relay may comprise an antenna coupled to the downholereceiver, the antenna being configured to receive electromagneticradiation. The casing data relay may comprise one or more casing sensorscoupled to the casing, wherein one or more of the one or more casingsensors are coupled to the transmitter. The casing data relay maycomprise one or more drill string sensors coupled to a drill string. Atleast a portion of the drill string may be inserted through the casing.The drill string sensors may be coupled to the downhole receiver. One ormore of the drill string sensors may be coupled to the downhole receiverthrough a drill string transmitter. The casing data relay may comprisedrill string instruments coupled to the transmitter and a surfacetransmitter coupled to the downhole receiver. The casing data relay maycomprise a drill string actuator. The drill string actuator may becontrollable through the downhole receiver. The drill string actuatormay be configured to change a position of an adjustable gaugestabilizer. The drill string actuator may be configured to change a bitnozzle size.

[0015] In general, in another aspect, the invention features a methodfor collecting geological data comprising sensing one or more geologicalparameters during drilling using one or more sensors coupled to a wellcasing in a well bore, collecting data from the one or more sensors andtransmitting the data to the surface. Sensing may comprise sensing usingone or more sensors coupled to a casing shoe, sensing using a pressuretransducer on a casing shoe, sensing pressure, sensing temperature,sensing acoustic energy, sensing stress or sensing strain. The methodmay further comprise transmitting acoustic energy. Transmitting maycomprise transmitting the data to the surface through a relay.

[0016] In general, in another aspect, the invention features a methodfor maintaining the integrity of a formation in the vicinity of a casingshoe comprising measuring well bore pressure in the vicinity of thecasing shoe during drilling.

[0017] Implementations of the invention may include one or more of thefollowing. The method may comprise transmitting data representing themeasured well bore pressure to the surface.

[0018] In general, in another aspect, the invention features a methodfor positioning look ahead sensors comprising positioning acousticsensors along a casing string.

[0019] In general, in another aspect, the invention features a methodfor monitoring well control events comprising monitoring pressure at twoor more locations inside a casing of the well.

[0020] Implementations of the invention may include one or more of thefollowing. Monitoring may comprise monitoring pressure at two or morelocations that are longitudinally displaced along the casing.

[0021] In general, in another aspect, the invention features a methodfor determining whether cement in a well borehole has cured comprisingpositioning a temperature sensor on a casing and monitoring thetemperature of the cement using the temperature sensor.

[0022] Implementations of the invention may include one or more of thefollowing. Positioning may comprise positioning the temperature sensorinside the casing or positioning the temperature sensor on the casingshoe.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023]FIG. 1 is a cross-section view of a drilling operation.

[0024]FIG. 2 is a cross-section view of casing being inserted into awell.

[0025]FIG. 3 is a perspective view of a section of casing according tothe present invention.

[0026]FIG. 4 is a perspective view of a section of casing according tothe present invention during the cementing operation.

[0027]FIG. 5 is a perspective view of a section of casing according tothe present invention.

[0028]FIG. 6 is a perspective view of a section of casing according tothe present invention after drilling has pierced the end of the casing.

[0029]FIG. 7 is a block diagram of a system according to the presentinvention.

[0030]FIG. 8 is a block diagram of a system according to the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] An apparatus for monitoring geological properties and drillingparameters and for facilitating seismic while drilling comprisessensors, actuators and generators coupled to the casing. The sensorsallow the collection and transmission to the surface of geological dataand critical drilling parameters (such as hydraulic measurements,downhole weight on bit, and downhole torque) from shortly after thecasing is inserted until the data is no longer needed. The actuators andgenerators facilitate the collection of data and are controllable fromthe surface. The apparatus also provides a relay for data transmittedfrom deeper in the well bore or from MWD or LWD tools. The equipmentrelays data between the surface and the sensors, actuators andgenerators deep in the well.

[0032] As shown in FIG. 1, a drilling rig 10 (simplified to excludeitems not important to this application) comprises a derrick 12, derrickfloor 14, draw works 16, hook 18, swivel 20, kelly joint 22, rotarytable 24, drillstring 26, drill collar 28, LWD tool 30, LWD tool 32 anddrill bit 34. Mud is injected into the swivel by a mud supply line 38.The mud travels through the kelly joint 22, drillstring 26, drillcollars 28, and LWD tools 30 and 32 and exits through jets or nozzles inthe drill bit 34. The mud then flows up the borehole 40. A mud returnline 42 returns mud from the borehole 40 and circulates it to a mud pit(not shown) and back to the mud supply line 38. The combination of thedrill collar 28, LWD tool 30, LWD tool 32 and drill bit 34 is known asthe bottomhole assembly 36 (or “BHA”).

[0033] The data collected by the LWD tools 30 and 32 is returned to thesurface for analysis by, for example, telemetry transmitted through thedrilling mud. A telemetry transmitter 44 located in a drill collar or inone of the LWD tools collects data from the LWD tools and modulates thedata to transmit it through the mud. A telemetry sensor 46 on thesurface detects the telemetry and returns it to a demodulator 48. Thedemodulator 48 demodulates the data and provides it to computingequipment 50 where the data is analyzed to extract useful information.

[0034] After the well has been drilled to a certain depth, has shown inFIG. 2, a length of casing 52 is lowered into the well bore in sections.The first section 54, called a “casing shoe”, has a specialized purpose,as will be discussed below. As it is being lowered, the section ofcasing is suspended from casing hangar 56, which hangs from the hook 18.

[0035] When the casing 52 has been fully inserted into the borehole, asshown in FIG. 3, the casing shoe 54 comes to rest at or near the bottomof the well bore. A centralizer 58 keeps the casing centered in theborehole. Signal-carrying cable 60 connects a cable tie in 62 toequipment on the surface. The cable 60 and cable tie-in 62 allow aconnection 65 between the surface and sensors, actuators and generatorsin the casing shoe, as will be discussed below. Further, cable 60provides connections between sensors, actuators and generators locatedalong the casing (not shown in FIG. 3) to the casing shoe 54. Wirelineanchor bands 64 secure the cable 60 to the casing.

[0036] After the casing is position, it is cemented into place, as shownin FIG. 4. Cement is pumped down through the casing to the casing shoewhere it escapes through port 66. The cement 68 flows up the annulusbetween the casing and the surrounding formations 70.

[0037] When sufficient concrete has been poured to serve its intendedpurpose, the concrete is allowed to set, as shown in FIG. 5. As concretesets, its temperature varies. By monitoring the temperature of theconcrete using temperature sensor 72, personnel at the surface candetermine when the concrete has set sufficiently to go into the nextstep in the drilling process. Information from the temperature sensor 72is transferred to the surface through cable tie-in 62 and cable 60.Additional temperature sensors may be placed at other locations tomonitor the temperature of the concrete.

[0038] The next step in the drilling process, shown in FIG. 6, is todrill out casing 52. Drill bit 74 penetrates the end of casing shoe 54and continues the well bore. As drilling continues, mud is pumped downthrough the center of the drillstring 76 and out jets or nozzles in thedrill bit 74. The mud 78 picks up cuttings and carries them back tosurface along the annulus between the drill string and formation andthen along the annulus between the drillstring 76 and casing 52.

[0039] As discussed above, the specific gravity of the mud is carefullycontrolled to assure that the pressure exerted by the mud on theformation does not exceed the fracture pressure of formation. Thepressure exerted by the mud on the formation is monitored by a pressuresensor 80 located in the casing shoe. Its location in the casing shoeallows pressure sensor 80 to monitor the pressure on the weakestformation just below the casing shoe.

[0040] Personnel on the surface monitor the signals from the pressuresensor, which are sent to the surface through the cable tie-in 62 andcable 60. If they determine that the specific gravity of the mud must beincreased because of the danger of a “kick”, or influx of formationfluids into the borehole, and the planned increase will raise thepressure exerted by the mud beyond the fracture pressure of theformation, they may decide to stop drilling and insert another sectionof casing.

[0041] In addition to the pressure sensor and temperature sensor thatwere discussed above, additional sensors are located along the casing toprovide a variety of other functions. For example, an array of acousticsensors and/or geophones may be located along a portion of the casing toreceive acoustic energy from the formation through the concretesurrounding the casing. Such acoustic sensors could be used inconjunction with acoustic energy generators located in the MWD tools foraccomplishing MWD acoustic logging. The acoustic energy generator couldbe attached to the casing, allowing long term monitoring of the acousticcharacteristics of the formations surrounding the borehole. An acousticenergy generator attached to the casing could also be used as a sourcefor acoustic energy measurements in another nearby well.

[0042] Similarly, the acoustic sensors could be used to detect acousticenergy generated by surface generators or by acoustic sources in othernearby wells. The acoustic sensors could be used during drilling andafter the well is completed and is in production or after it has beenshut in.

[0043] Acoustic sensors coupled to the casing can also be used insupport of “look-ahead” technology, in which acoustic signals are usedto detect geological features ahead of the drill bit. With the acousticsensors coupled to the casing, the look-ahead performance improves overa look-ahead system employing surface acoustic sensors because theacoustic sensors coupled to the casing are closer to the geologicalfeatures being detected.

[0044] In addition to pressure sensors, temperature sensors and acousticsensors and generators, stress and strain sensors may be located alongthe casing to measure the stress and strain to be experienced by theformations surrounding the casing. Again, the stress sensors and strainsensors can be used during drilling and after the well has beencompleted and has been placed in production or has been shut in.

[0045] In another application of sensors, two or more pressure sensorscould be strategically located at various depths along the inside of thecasing. Such an arrangement of pressure sensors could detect the dynamicchanges in pressure associated with a kick. For example, detection ofdropping pressure at successively shallower pressure sensors couldindicate that a gas kick has occurred. Advance warning of such an eventwould allow personnel on the surface to engage blowout preventers toreduce the chance of injury to the surface equipment or personnel.

[0046] In general, any sensor that provides useful information regardingthe formations surrounding the well can be attached to the casing.Further, any actuator or generator that produces useful signals, energyor actions to be used in measuring the properties of the formations orin monitoring the drilling process may also be attached to the casing.

[0047] The placement of the sensors, actuators and generators isillustrated in FIG. 7. The well shown in FIG. 7 includes a surfacecasing 82, an intermediate casing 84, and a drill string 86. A set ofsurface casing sensors, actuators and generators 88 is coupled to thesurface casing 82. A set of intermediate casing sensors, actuators andgenerators 90 is coupled to the intermediate casing 84. Depending ontheir purpose, the sensors, actuators and generators may be attached tothe inside of the casing or the outside of the casing. The sensors,actuators and generators may be welded to the casing or attached bybands or through special annular fittings that affix them to the insideor the outside of the casing in such a way that they do not interruptthe flow of fluids through or around the casing.

[0048] A set of MWD tool sensors, actuators and generators 92 is coupledto the drill string 86. For example, if the MWD tool is anacoustic-logging tool, it would include acoustic energy generators(transmitters) and acoustic energy sensors (receivers). Other types oftools would include other types of sensors and generators. The MWD toolsensors, actuators and generators 92 may provide, for example, thecapability to change the position of an adjustable gauge stabilizer orto change the bit nozzle size or to activate any actuator attached tothe drill string.

[0049] The sensors, actuators and generators communicate with thesurface in one or more of several ways. First, each sensor, actuator orgenerator may have a cable connection to the surface. For example, thesurface casing sensors, actuators and generators 88 may communicate withsurface equipment 94 via cable 96 and the intermediate casing sensors,actuators and generators 90 may communicate with the surface equipment94 via cable 98. Alternatively, some or all of the surface casingsensors, actuators and generators 88 may communicate with a surfacecasing controller 100, coupled to the surface casing 82, which gathersdata provided by the surface casing sensors, formats it and communicatesit to the surface equipment 94 via cable 98. Surface equipment 94 maytransmit commands or other data to the surface casing sensors, actuatorsand generators 88 directly or through the surface casing controller 100.

[0050] Similarly, some or all of the intermediate casing sensors,actuators and generators 90 may communicate with an intermediate casingcontroller 102, coupled to the intermediate casing 84, which gathersdata provided by the intermediate casing sensors, formats it andtransmits it to the surface equipment 94. Surface equipment 94 maytransmit commands or other data to the intermediate casing sensors,actuators and generators 90 directly or through the intermediate casingcontroller 102.

[0051] Cables 96 and 98 can be any kind of cable, including electricalcable or optical fiber cable. Further, the information carried by thecable can be sent using any information transmission scheme, includingbaseband, modulated (amplitude modulation, frequency modulation, phasemodulation, pulse modulation or any other modulation scheme), andmultiplexed (time-division multiplexed, frequency-division multiplexedor any other multiplexing scheme, including the use of spread spectrumtechniques). Consequently, each sensor, actuator or generator maycommunicate with the surface equipment via its own communication mediawhich is part of cables 96 and 98 or each set 88 and 90 may share acommunication media that is part of cables 96 and 98, respectively.Further, cables 96 and 98 may be coupled to allow the surface casingsensors, actuators and generators to share the use of the communicationmedium formed by the combination of the two cables 96 and 98.

[0052] Alternatively, communication between the surface casingcontroller 100 and the surface equipment 94 may be by radio frequencytransmission or pulse telemetry transmission. In the case of radiofrequency transmission, an antenna 104 extends from the surface casingcontroller 100 that allows radio frequency communication between it andthe surface equipment 94, which would communicate the RF energy via anantenna 106. In the case of pulse telemetry transmission, the surfacecasing controller 100 and the surface equipment 94 each include atransducer 108 and 110 (see FIG. 8), respectively, that convert datainto acoustic pulses and vice versa. The acoustic energy travels throughthe casing 82, the mud or any other medium that will allow thetransmission of acoustic energy. The RF energy and the acoustic energycan be modulated or multiplexed in any of the ways described above.Further, the communication between the surface casing controller 100 andthe surface equipment 94 may be done through a combination ofcommunication through the cable, through RF transmission and throughpulse telemetry.

[0053] Communication between the intermediate casing controller 102 andthe surface equipment 94 can be by any of the methods described abovefor the communication between the surface casing controller 100 and thesurface equipment 94. An antenna 112 is coupled to the intermediatecasing controller 102 to allow RF communication. An acoustic transducer114 (see FIG. 8) is coupled to the intermediate casing controller 102 toallow pulse telemetry communication. Alternatively, the surface casingcontroller 100 can serve as a relay between the intermediate casingcontroller 102 and the surface equipment 94. In this situation, theintermediate casing controller 102 communicates with the surface casingcontroller 100 using any of the communication techniques discussedabove, including communicating by cable, by RF transmission or by pulsetelemetry. The surface casing controller 100 communicates with thesurface equipment 94 as discussed above.

[0054] The MWD tool sensors, actuators and generators 92 communicatewith the surface equipment 94 through a drill string controller 116. Thedrill string controller 116 compiles data from the MWD tool sensors,actuators and generators 92 and transmits the data to the surfaceequipment 94. The surface equipment 94 transmits commands and other datato the MWD tool sensors, actuators and generators 92 through the drillstring controller 116. The communication between the surface equipment94 and the drill string controller 116 may be relayed through theintermediate casing controller 102 and the surface casing controller100. Alternatively, the drill string controller 116 may only use one ofthe surface casing controller 100 or the intermediate casing controller102 as a relay. The communication between the drill string controller116 and the surface equipment 94 may use any of the informationtransmission schemes described above. An antenna 118 is coupled to thedrill string controller 116 to allow RF communication. An acoustictransducer 120 (see FIG. 8) is coupled to the drill string controller116 to allow pulse telemetry communication.

[0055]FIG. 8 illustrates all of the communication paths possible amongthe various sensors, actuators, generators, controllers and surfaceequipment. In the preferred embodiment, the surface casing sensors,actuators and generators 88 communicate with the surface casingcontroller 100 which communicates with the surface equipment 94 overcable 96. Alternatively: (a) one or more of the surface casing sensors,actuators and generators 88 may communicate directly with the surfaceequipment 94, as indicated by dotted line 122; (b) communication betweenthe surface casing controller 100 and the surface equipment 94 may be byRF signals using antennas 104 and 106 or by pulse telemetry usingacoustic transducers 108 and 110.

[0056] In the preferred embodiment, the intermediate casing sensors,actuators and generators communicate with the intermediate casingcontroller 102 which communicates with the surface equipment 94 by RFsignals using antennas 104 and 112 or by pulse telemetry using acoustictransducers 108 and 114. Alternatively: (a) one or more of theintermediate casing sensors, actuators and generators 90 may communicatedirectly with the surface equipment 94, as indicated by dotted line 124;(b) communication between the intermediate casing controller 102 and thesurface equipment 94 may be by way of cable 98 (shown as a dotted line).

[0057] In the preferred embodiment, the drill string sensors, actuatorsand generators 92 communicate directly with the drill string controller116, which may be part of an MWD tool or some other piece of drillstring equipment. The drill string controller 116 communicates with thesurface equipment 94 through antenna 118 and/or acoustic transducer 120directly or using the intermediate casing controller 102 and/or thesurface casing controller 100 as relays.

[0058] The foregoing describes preferred embodiments of the inventionand is given by way of example only. The invention is not limited to anyof the specific features described herein, but includes all variationsthereof within the scope of the appended claims.

What is claimed is:
 1. A casing sensor comprising a casing shoe; asensor coupled to the casing shoe.
 2. The casing sensor of claim 1wherein the sensor comprises a pressure sensor.
 3. The casing sensor ofclaim 2 wherein the pressure sensor comprises a pressure transducer; anda transmitter coupled to the pressure transducer.
 4. The casing sensorof claim 1 further comprising a surface receiver coupled to thetransmitter.
 5. The casing sensor of claim 1 further comprising a drillstring through the casing shoe.
 6. A casing data relay comprising adownhole receiver coupled to a well casing; and a transmitter coupled tothe receiver.
 7. The casing data relay of claim 6 further comprising asurface receiver coupled to the transmitter.
 8. The casing data relay ofclaim 7 wherein the surface receiver is electrically coupled to thetransmitter.
 9. The casing data relay of claim 7 wherein the surfacereceiver is optically coupled to the transmitter.
 10. The casing datarelay of claim 7 wherein the surface receiver is coupled to thetransmitter by electromagnetic telemetry.
 11. The casing data relay ofclaim 7 wherein the surface receiver is coupled to the transmitter by apressure transducer.
 12. The casing data relay of claim 6 furthercomprising an antenna coupled to the downhole receiver; the antennabeing configured to receive electromagnetic radiation.
 13. The casingdata relay of claim 6 further comprising one or more casing sensorscoupled to the casing; one or more of the one or more casing sensorsbeing coupled to the transmitter.
 14. The casing data relay of claim 6further comprising one or more drill string sensors coupled to a drillstring, at least a portion of the drill string being inserted throughthe casing; the drill string sensors being coupled to the downholereceiver.
 15. The casing data relay of claim 14 wherein one or more ofthe drill string sensors are coupled to the downhole receiver through adrill string transmitter.
 16. The casing data relay of claim 6 furthercomprising drill string instruments coupled to the transmitter; and asurface transmitter coupled to the downhole receiver.
 17. The casingdata relay of claim 6 further comprising a drill string actuator; thedrill string actuator being controllable through the downhole receiver.18. The casing data relay of claim 17 wherein the drill string actuatoris configured to change a position of an adjustable gauge stabilizer.19. The casing data relay of claim 17 wherein the drill string actuatoris configured to change a bit nozzle size.
 20. A method for collectinggeological data comprising sensing one or more geological parametersduring drilling using one or more sensors coupled to a well casing in awell bore; collecting data from the one or more sensors; andtransmitting the data to the surface.
 21. The method of claim 20 whereinsensing comprises sensing using one or more sensors coupled to a casingshoe.
 22. The method of claim 20 wherein sensing comprises sensing usinga pressure transducer on a casing shoe.
 23. The method of claim 20wherein sensing comprises sensing pressure.
 24. The method of claim 20wherein sensing comprises sensing temperature.
 25. The method of claim20 wherein sensing comprises sensing acoustic energy.
 26. The method ofclaim 20 further comprising transmitting acoustic energy.
 27. The methodof claim 20 wherein sensing comprises sensing strain.
 28. The method ofclaim 20 wherein sensing comprises sensing stress.
 29. The method ofclaim 20 wherein transmitting comprises transmitting the data to thesurface through a relay.
 30. A method for maintaining the integrity of aformation in the vicinity of a casing shoe comprising measuring wellbore pressure in the vicinity of the casing shoe during drilling. 31.The method of claim 30 further comprising transmitting data representingthe measured well bore pressure to the surface.
 32. A method forpositioning look ahead sensors comprising positioning acoustic sensorsalong a casing string.
 33. A method for monitoring well control eventscomprising monitoring pressure at two or more locations inside a casingof the well.
 34. The method of claim 33 wherein monitoring comprisesmonitoring pressure at two or more locations that are longitudinallydisplaced along the casing.
 35. A method for determining whether cementin a well borehole has cured comprising positioning a temperature sensoron a casing; and monitoring the temperature of the cement using thetemperature sensor.
 36. The method of claim 35 wherein positioningcomprises positioning the temperature sensor inside the casing.
 37. Themethod of claim 35 wherein position comprises positioning thetemperature sensor on the casing shoe.